Set max path len on receipt of static invoice.

We don't want to wait until we actually go to send HTLCs to do this check,
since that could be days later.

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -4292,9 +4292,11 @@ where
 	) -> Result<(), Bolt12PaymentError> {
 		let mut res = Ok(());
 		PersistenceNotifierGuard::optionally_notify(self, || {
+			let best_block_height = self.best_block.read().unwrap().height;
 			let features = self.bolt12_invoice_features();
 			let outbound_pmts_res = self.pending_outbound_payments.static_invoice_received(
-				invoice, payment_id, features, &*self.entropy_source, &self.pending_events
+				invoice, payment_id, features, best_block_height, &*self.entropy_source,
+				&self.pending_events
 			);
 			let payment_release_secret = match outbound_pmts_res {
 				Ok(secret) => secret,

lightning/src/ln/outbound_payment.rs

@@ -919,7 +919,7 @@ impl OutboundPayments {
 	#[cfg(async_payments)]
 	pub(super) fn static_invoice_received<ES: Deref>(
 		&self, invoice: &StaticInvoice, payment_id: PaymentId, features: Bolt12InvoiceFeatures,
-		entropy_source: ES,
+		best_block_height: u32, entropy_source: ES,
 		pending_events: &Mutex<VecDeque<(events::Event, Option<EventCompletionAction>)>>
 	) -> Result<[u8; 32], Bolt12PaymentError> where ES::Target: EntropySource {
 		macro_rules! abandon_with_entry {
@@ -961,7 +961,16 @@ impl OutboundPayments {
 					let payment_hash = PaymentHash(Sha256::hash(&keysend_preimage.0).to_byte_array());
 					let payment_release_secret = entropy_source.get_secure_random_bytes();
 					let pay_params = PaymentParameters::from_static_invoice(invoice);
-					let route_params = RouteParameters::from_payment_params_and_value(pay_params, amount_msat);
+					let mut route_params = RouteParameters::from_payment_params_and_value(pay_params, amount_msat);
+
+					if let Err(()) = onion_utils::set_max_path_length(
+						&mut route_params, &RecipientOnionFields::spontaneous_empty(), Some(keysend_preimage),
+						best_block_height
+					) {
+						abandon_with_entry!(entry, PaymentFailureReason::UnexpectedError);
+						return Err(Bolt12PaymentError::SendingFailed(RetryableSendFailure::OnionPacketSizeExceeded))
+					}
+
 					*entry.into_mut() = PendingOutboundPayment::StaticInvoiceReceived {
 						payment_hash,
 						keysend_preimage,